1. Technical Field of the Invention
The embodiments of the invention relate to communication devices and more particularly to a voltage controlled oscillator (VCO) based synthesizer implemented within such communication devices that uses a single VCO for generating local oscillation frequencies.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Communication systems typically operate in accordance with one or more communication standards. For instance, wired communication systems may operate according to one or more versions of the Ethernet standard, the System Packet Interface (SPI) standard, or various other standards. Wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). Typically, the transceiver includes a data modulation stage and an RF stage. The data modulation stage (baseband process) converts between data and baseband signals in accordance with the particular wireless communication standard. The RF stage (transmitter section and receiver section) converts between baseband signals and RF signals. The RF stage may be a direct conversion transceiver that converts directly between baseband and RF or may include one or more intermediate frequency stages.
Wireless devices typically operate within certain RF frequency ranges established by one or more communications standards or protocols. A local oscillator generally provides a local oscillation signal that is used to mix with received or transmitted signals in the modulation/demodulation stages. A synthesizer may be used to set the frequencies to drive the local oscillator to provide the desired frequencies for mixing, in which the desired frequencies are generally based on the channel frequencies established for the particular standard or protocol.
When synthesizers are designed to provide certain frequencies, phase locked loops (PLLs) may be used to control the frequency. Some problems encountered with PLL related technology include the phase noise not being sufficiently low, reference frequency for phase frequency detection not being sufficiently high, which may result in smaller loop bandwidth, and the phase noise from a voltage controlled oscillator (VCO) not having sufficient filtering. In some synthesizers, multiple VCOs may be employed to generate local oscillation signals for frequency channels that are separated in different bands.
Although PLLs have been utilized in various capacities to control frequencies, there is a need to improve the architecture for providing PLLs in frequency ranges employed by wireless communication devices and standards to increase performance and/or to alleviate or reduce some of the problems noted above. Furthermore, when communication devices employ capabilities to operate using more than one communication standard or frequency band, it may be advantageous to utilize one circuitry to provide for the more than one standard or frequency band. For example, many communication devices are designed to operate using different frequency channels of the 802.11 standard, such as 802.11a, 802.11b and 802.11g. Instead of having different circuitry to provide for different bands of channel frequencies, it may be advantageous to have a single circuit to provide for these frequency requirements.